In the tools menu (⌘) there are the 2 commands "Save current rules" and "Load saved rules". They act like Copy / Paste to copy the rules from one playlist (say A) to another playlist (say B). (In the next version of SmartPlaylist they will be named "Copy current rules" / "Paste copied rules" to clarify their purpose).
The rules of a playlist are (only) saved when the query is started with "Enter" (⏎), so that you can always see what is actually "inside" the list. So, if you change the rules and switch to another playlist without using "⏎", then those changes are not saved.